MCAS and POTS: Why These Two Conditions Travel Together

MCAS and POTS: Why These Two Conditions Travel Together

MCAS and POTS occur together because mast cell mediators and connective tissue laxity act on the same blood vessels and autonomic nerves that control heart rate and blood pressure. Clinical series report that mast cell activation syndrome affects an estimated 30 to 65 percent of people diagnosed with postural orthostatic tachycardia syndrome, an overlap first characterized in a 2019 study in the Journal of Allergy and Clinical Immunology.

You have been diagnosed with POTS. You manage the tachycardia, the lightheadedness, the salt loading, and the compression garments. But certain symptoms do not fit neatly into the POTS box: flushing episodes that come out of nowhere, GI symptoms that shift daily, hives after a hot shower, brain fog that persists regardless of hydration status. Your autonomic neurologist says those are not POTS symptoms. Your allergist says you do not have traditional allergies. And yet the symptoms are very real.

If you are nodding along, there is a strong chance that mast cell activation syndrome is running alongside your POTS and has not yet been identified. The overlap between these two conditions is far more common than most patients realize, and understanding why they travel together changes the treatment equation.

The Connection: How Mast Cells Affect the Autonomic Nervous System

Mast cells are immune sentinel cells distributed throughout your body, with especially high concentrations around blood vessels, in the gut lining, and in the skin. When they activate (degranulate), they release a cocktail of chemical mediators including histamine, prostaglandins, leukotrienes, tryptase, heparin, and various cytokines. Under normal conditions, this release is tightly controlled and serves protective functions. In MCAS, the activation threshold drops, and mast cells begin releasing mediators in response to stimuli that should not trigger them.

Several of these mediators have direct effects on the cardiovascular and autonomic systems:

• Histamine causes vasodilation (widening of blood vessels), which drops blood pressure and triggers a compensatory increase in heart rate. This mimics or worsens the orthostatic intolerance seen in POTS.
• Prostaglandin D2 is a potent vasodilator that can cause flushing, hypotension, and tachycardia.
• Tryptase at elevated levels can activate protease-activated receptors on blood vessel walls, influencing vascular permeability and tone.
• Heparin released from mast cells can affect blood coagulation and vascular function.
• Leukotrienes promote bronchoconstriction and can contribute to the air hunger some POTS patients experience.

The net result: when mast cells degranulate, they can produce acute episodes of vasodilation, blood pressure drops, and reflex tachycardia that look exactly like a POTS flare. For many patients, what gets labeled as a “POTS episode” is actually a mast cell-mediated event, or a combination of both processes feeding each other in a vicious cycle.

The terminology around this overlap can be confusing because it draws on several related but distinct fields. POTS is one specific subtype of dysautonomia, the broad term for autonomic nervous system dysfunction, and some patients also carry a hyperadrenergic POTS subtype marked by elevated standing norepinephrine. MCAS is sometimes called mast cell activation disorder (MCAD) in older literature, and it is distinct from mastocytosis, a rarer condition involving an actual increase in mast cell numbers rather than an abnormally low activation threshold. Evidence connecting mast cell signaling to autonomic regulation is still developing, and specialists in dysautonomia treatment increasingly screen new POTS patients for mast cell involvement rather than waiting for a second diagnosis to surface on its own.

How Common Is the Overlap?

The co-occurrence of MCAS and POTS is well documented, though exact numbers depend on the diagnostic criteria used and the population studied.

A 2019 study published in the Journal of Allergy and Clinical Immunology found that patients with POTS had significantly higher rates of mast cell mediator elevation compared to healthy controls. Other clinical series have reported that 30 to 65% of POTS patients meet criteria for MCAS when systematically evaluated. Some mast cell specialists believe the true overlap is even higher, because mast cell mediator testing is notoriously unreliable due to strict handling requirements for blood and urine samples.

The connection runs in both directions. Not only do many POTS patients have undiagnosed MCAS, but many MCAS patients develop autonomic dysfunction that meets POTS criteria. This bidirectional relationship suggests shared underlying mechanisms rather than a coincidental association. Readers who want a closer look at how each condition is evaluated on its own can start with how clinicians approach POTS diagnosis and how they approach MCAS diagnosis before mapping the two together.

The Triad: MCAS, POTS, and EDS

Clinicians who work with these patient populations have long noticed a three-way overlap between MCAS, POTS, and hypermobile Ehlers-Danlos syndrome (hEDS). This triad appears so frequently that some researchers now view it as a distinct clinical phenotype rather than three separate conditions that happen to coexist.

This triad model has practical implications. If you have been diagnosed with one of these three conditions, proactive screening for the other two can prevent years of unnecessary diagnostic wandering. Patients who do not meet the full criteria for hEDS sometimes fall under the related label of hypermobility spectrum disorder (HSD), and the same triad logic generally applies to them as well. For a dedicated look at how the three conditions interact, see our guide to the MCAS, POTS, and EDS triad, and for background on the joint hypermobility piece of the picture, see our overview of EDS symptoms.

Diagnostic Challenges: Where Symptoms Overlap

Disentangling MCAS symptoms from POTS symptoms is one of the most challenging aspects of managing both conditions. The following table highlights common symptoms and which condition (or both) may be responsible.

The pattern to watch for: if your POTS symptoms are episodic and unpredictable rather than purely positional, if you have symptoms that worsen with heat, stress, or certain foods, or if standard POTS treatments (salt, fluids, compression) help some symptoms but leave others untouched, MCAS should be on the differential.

Fibromyalgia and chronic fatigue syndrome are also frequent companions to this picture, since fatigue, brain fog, and widespread pain can stem from autonomic dysfunction, mast cell signaling, or both. If your symptom list includes diffuse pain or post-exertional crashes that the table above does not fully explain, it is worth discussing fibromyalgia with your care team alongside MCAS and POTS, and reviewing the broader pattern of dysautonomia symptoms that can accompany any of these diagnoses.

Getting Properly Diagnosed

Diagnosis of POTS is relatively straightforward: a sustained heart rate increase of 30 beats per minute or more (40 bpm in adolescents) within 10 minutes of standing, in the absence of orthostatic hypotension, with symptoms present for at least three months. A tilt table test or active standing test confirms the diagnosis.

MCAS diagnosis is more complex. The current consensus criteria require:

1. Recurrent episodes of symptoms consistent with mast cell mediator release affecting two or more organ systems
2. Objective evidence of mast cell mediator elevation (such as serum tryptase, 24-hour urinary histamine metabolites, prostaglandin D2, or urinary leukotriene E4)
3. Response to mast cell-directed therapy (antihistamines, mast cell stabilizers)

The challenge with criterion two is that mediator levels are often normal between flares, and samples must be collected during or shortly after a symptomatic episode with meticulous handling (chilled, processed rapidly). False negatives are extremely common, which is why many experienced clinicians will trial mast cell-directed therapy even when lab work is inconclusive.

Treatment: A Coordinated Approach

When MCAS and POTS coexist, treating one without addressing the other is like patching one tire on a car that has two flats. Coordinated treatment targeting both conditions simultaneously produces far better results. Evidence for several of the options below, especially supplements and off-label medications, is still developing, and many are cash pay and not FDA-approved for this specific use, so treatment decisions are best made with a physician who knows your full history, ideally one versed in dysautonomia treatment.

Mast Cell Stabilization

• H1 antihistamines: Cetirizine (Zyrtec) or fexofenadine (Allegra), often at higher-than-standard doses under medical supervision
• H2 antihistamines: Famotidine (Pepcid) to address GI symptoms and reduce gastric acid overproduction from histamine
• Mast cell stabilizers: Cromolyn sodium (oral, for GI symptoms) and ketotifen (oral, for systemic mast cell stabilization). Ketotifen has both antihistamine and mast cell-stabilizing properties.
• Quercetin: A flavonoid with mast cell-stabilizing properties. Typical dose: 500 to 1,000 mg twice daily.
• Low-dose aspirin: Blocks prostaglandin production from mast cells. Useful for flushing and some cardiovascular symptoms.

Autonomic Support (POTS-Directed)

• Volume expansion: Increased salt intake (3 to 10 grams daily), increased fluid intake (2 to 3 liters daily), and in some cases IV saline infusions, which some patients arrange through an IV therapy clinic under physician orders
• Compression garments: Waist-high compression stockings (30 to 40 mmHg) and abdominal binders reduce venous blood pooling
• Medications: Fludrocortisone (volume expansion), midodrine (vasoconstriction), propranolol or ivabradine (heart rate control)
• Exercise: Recumbent exercise programs (rowing, recumbent cycling, swimming) gradually build cardiovascular conditioning. The Levine/CHOP protocol is the most studied approach.

Treating the Overlap

Some interventions help both conditions simultaneously. Low-dose naltrexone (LDN) has immune-modulating properties that may stabilize mast cells while also supporting autonomic function. A low-histamine diet reduces the dietary histamine load that can trigger both mast cell and autonomic symptoms. Stress management techniques (vagal toning exercises, paced breathing, meditation, and structured biofeedback therapy) improve autonomic balance and may reduce mast cell reactivity.

Trigger avoidance is also a dual-purpose strategy. Many POTS triggers (heat, prolonged standing, dehydration) are also MCAS triggers. Identifying and managing personal triggers reduces flare frequency from both conditions.

Finding the Right Care Team

Managing MCAS and POTS together requires a care team that understands both conditions. An ideal team might include an immunologist or allergist with MCAS experience, an autonomic neurologist or cardiologist for POTS management, and a primary care provider willing to coordinate between specialists. Functional medicine practitioners with experience in complex, multi-system conditions can also serve as valuable coordinators.

The most important quality in a provider is willingness to treat the whole clinical picture rather than focusing on one diagnosis at a time. Patients with both MCAS and POTS often describe feeling like they are being treated by doctors who each see only a piece of the puzzle. A provider who recognizes the relationship between these conditions can save you years of fragmented care.

Frequently asked questions

Can you have POTS without MCAS, or MCAS without POTS?

Yes. POTS and MCAS are separate diagnoses with their own criteria, and many patients have only one condition. POTS is defined by an abnormal heart rate response to standing, while MCAS is defined by recurrent mast cell mediator release affecting multiple organ systems. The two conditions co-occur often enough that clinicians familiar with either one routinely screen for the other, but neither diagnosis requires the presence of the second.

What triggers both MCAS and POTS at the same time?

Heat, prolonged standing, dehydration, physical exertion, and emotional stress commonly trigger flares in both conditions at once, because they combine blood pooling with mast cell degranulation. Certain histamine-rich foods, alcohol, strong fragrances, and infections can also activate mast cells while simultaneously stressing the autonomic nervous system. Keeping a symptom and trigger log helps identify which combinations reliably produce the worst episodes for a given patient.

Does treating MCAS improve POTS symptoms?

Many patients notice fewer tachycardia episodes and less lightheadedness once mast cell mediator release is controlled with antihistamines or mast cell stabilizers, because histamine and prostaglandin D2 directly cause vasodilation and reflex heart rate increases. Improvement is usually partial rather than complete, since POTS also involves blood volume regulation and nerve signaling that mast cell treatment does not address. Most clinicians recommend treating both conditions together rather than expecting one treatment to resolve both.

What tests confirm MCAS and POTS together?

POTS is confirmed with a tilt table test or an active standing test showing a sustained heart rate rise of at least 30 beats per minute within 10 minutes of standing. MCAS testing looks for elevated mast cell mediators, such as serum tryptase or urinary prostaglandin D2 and leukotriene E4, ideally collected during a flare. Because mediator levels often normalize between episodes, a negative test does not rule out MCAS, and many clinicians also weigh response to mast cell-directed therapy.

Is MCAS and POTS the same as dysautonomia?

No. Dysautonomia is a broad umbrella term for any dysfunction of the autonomic nervous system, and POTS is one specific type of dysautonomia. MCAS is not a form of dysautonomia at all; it is an immune condition involving inappropriate mast cell activation, though its mediators can produce autonomic-like symptoms. Patients with EDS, POTS, and MCAS may hear all three terms used loosely, but each has distinct diagnostic criteria.

Related Reading

• Mast Cell Activation Syndrome (MCAS): The Complete Patient Guide
• POTS Treatment: Evidence-Based Approaches
• Ehlers-Danlos Syndrome: Getting the Right Diagnosis
• POTS Diet: What to Eat for Autonomic Support
• MCAS Guide: From Diagnosis to Daily Management
• The MCAS, POTS, and EDS Triad Explained
• Recognizing Dysautonomia Symptoms